The present invention relates to a method for suppression of electrification and in particular to a method for suppression of electrification in electron beam writing, observation, and linewidth measurement using charged particle-beams such as an electron beam, etc. and also in ion implantation.
In pattern formation using charged particle-beams such as an electron beam, an ion beam, etc. especially when an insulating substrate is used, the substrate is electrified and the orbit of incident charged particle-beam is deflected by the electric field formed by charges in the substrate. Thus, there is a problem of inaccurate positioning of patterns to be formed.
Furthermore, in observation instruments using charged particle beams such as an electron beam microscope and an electron beam linewidth measurement system, distortion of observed image or inaccurate linewidth measurement occurs owing to the substrate electrification phenomenon. Moreover, in the ion implantation technique used for introducing impurities into a semiconductor substrate, dielectric breakdown of an oxide film deposited on the substrate sometimes occurs due to the electrification phenomenon, when the ion implantation is carried out at a high concentration, resulting in a failure in breakdown voltage of gate electrodes in MOS field effect transistors.
Hitherto, many methods for reducing the electrification of substrates in the electron beam writing are known. For example, the electrification effect can be eliminated most simply by deposition of a thin metal film by evaporation onto the substrate destined for the writing prior to the electron beam writing.
Furthermore, it is known to form a chloromethylpolystyrene layer as an underlayer on an electron beam resist [Japanese Patent Application Kokai (Laid-Open) No. 63-129622]. Since the chloromethylpolystyrene turns electroconductive when irradiated with an electron beam, the injected electrons migrate to the conducting substrate without electrification of the underlayer.
Japanese Patent Application Kokai (Laid-Open) No. 1-132122 discloses a method for forming a water-soluble, electrification-suppressing film on an electron beam resist. The method has such an advantage that the water-soluble compounds have no influence upon the resist at the coating and removal.
The above-mentioned prior art of depositing a thin metal film by evaporation has such problems as complicatedness in the deposition by evaporation and contamination by metal elements in case of semiconductor devices.
Furthermore, the prior art disclosed in the above-mentioned Japanese Patent Application Kokai (Laid-Open) No. 63-129622 is not effective for suppressing the electrification when the substrate is coated with a silicon oxide film or the substrate itself has an insulating property.
Moreover, the prior art disclosed in the above-mentioned Japanese Patent Application Kokai (Laid-Open) No. 1-132122 has such a problem as slow charge transfer because the disclosed materials are ion-conducting. Therefore, it is difficult to obtain a sufficient electrification-suppressing effect in the high-speed electron beam writing.